1. Field of the Invention
This invention relates to computer graphics display systems, and more particularly relates to such a graphics computer system that employs parallel processors in a display processor portion thereof.
2. Background Art
Besides Lines, Markers and Polygons, Computer Graphics Displays today support more general geometric primitives, such as Spline Curves and Spline Surfaces.
In the Computer Aided Design/Computer Aided Manufacture ("CAD/CAM") area, most of the geometric data can be covered by using Non-Uniform Rational B-Spline of degree less than or equal to three-linear, quadratic or cubic (see the sections below). For Non-Uniform Rational B-Spline Surfaces, there exist techniques to break up the surface into simpler Rational Bezier Surface Patches.
A system is described herein which uses Parallel Processors to implement the display function of Rational Bezier Surface patches for both wireframe model and solid/shaded model. The use of Parallel Processors to implement display functions in computer graphics system has been described generally in an article by James Clark of Stamford University, "A VLSI Geometry Processor for Graphics," Clark, James, COMPUTER, Jul. 1980, pp. 59-68.
U.S. Pat. No. 4,187,539 to Eaton describes a pipelined data processing system with centralized microprogram control.
However, absent in the prior art is a processing system that permits efficient parallel and pipelined processing for generating surface information for a graphics display system. Prior art arrangements require complicated and extensive external control logic, where attempts have been made to combine a number of processors together in graphics processing. As a result, progress heretofore in the area of more efficient processing in workstations of graphics computer systems has been limited.
For example, conventionally CAD/CAM applications use graphics workstations by sending down the polygons which make up the objects stored in the host computer data base, rather than the Spline surface form data stored in the data base. According to this procedure, the host computer decomposes the Spline surface into flat polygons, and then sends the polygons to the graphics workstation. The graphics workstation then processes the polygons for display.
The drawbacks of this approach are several. First, the host processor takes more time to do the Spline surface decomposition than would be desired. Second, by requiring the host processor to generate the data corresponding to the polygons, more data must be sent between the host processor and the graphics workstation. This ties up the transmission link which may be sharing with other applications and graphics workstations. Thirdly, when local zooming is applied to the polygonal data, the display of the model loses its smoothness. As a result, the program in the graphics workstation must notify the host computer to decompose the surface data and send the polygon again, to restore the smoothness of the object being zoomed.
Accordingly, it is an object of the present invention to provide a processing system that generates surface information for a graphics display system.
It is a further object of the invention to provide a processing system wherein the processing to generate surface information is performed in parallel, pipelined fashion.
It is a still further object of the present invention to provide a processing system in which surface information is generated according to rational B Spline computation in an efficient manner.
It is a still further object of the present invention to provide a processing system in which Spline surface computation of polygons can be performed in a graphics workstation, rather than in a host processor.